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STP/Port Channel question

Hi All,

Basic question on Port channel/STP.

Core Switch A : STP root      Core SW B : STP Secondary. : Core A&B port channeled (PO#1)

Access SW1(STP priority set to Max) : connected to Core SW A via PO# 10 (ports gig 0/19 & 20)

SW1 also connects to Core SW B via PO#20 (porta gig 0/23 & 24) for redundancy.

So in this scenario, will the Core SW B ports that connected to SW1 (via PO#20) will be blocked to avoid the loop or not?

Thanks in advance

MS

2 ACCEPTED SOLUTIONS

Accepted Solutions
Hall of Fame Super Silver

Re: STP/Port Channel question

Hello MS,

bundle  20 will be blocked but on the access layer switch side: its STP priority is worse then that of CoreB, CoreB will be elected designated port on the segment, as a result of this access layer switch should be in blocking state.

Be aware that if the bundle is a L2 trunk and you have developed different STP priorities for different vlans on core A and core B you will be able to use both bundle 10 and bundle 20 for different sub sets of vlans. (all this if STP mode is per vlan STP PVST+ that is the default)

Hope to help

Giuseppe

Re: STP/Port Channel question

Hi ,

Port channel connected to core sw B will be in blocked state at access layer switch end  and port at core sw B will be DP !!

Regards

Ganesh.H

3 REPLIES
Hall of Fame Super Silver

Re: STP/Port Channel question

Hello MS,

bundle  20 will be blocked but on the access layer switch side: its STP priority is worse then that of CoreB, CoreB will be elected designated port on the segment, as a result of this access layer switch should be in blocking state.

Be aware that if the bundle is a L2 trunk and you have developed different STP priorities for different vlans on core A and core B you will be able to use both bundle 10 and bundle 20 for different sub sets of vlans. (all this if STP mode is per vlan STP PVST+ that is the default)

Hope to help

Giuseppe

Re: STP/Port Channel question

Hi ,

Port channel connected to core sw B will be in blocked state at access layer switch end  and port at core sw B will be DP !!

Regards

Ganesh.H

Re: STP/Port Channel question

Thank you all for the clarification.

MS

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